The present invention relates to a pulse driven synchronous machine using a permanent magnet for producing a field in which the rotor is made of toothed and laminated iron core and the stator is attached with permanent magnets forming a field at the surface facing the air gap between the rotor and the stator, and in which multi-phase distributed windings are wound in the stator grooves.
The present invention further relates to a permanent magnet type linear stepping motor utilizing the armature as an inductor and utilizing plural permanent magnets for producing a field.
Conventionally, a permanent magnet field type synchronous machine, e.g., a hybrid type stepping motor is of a homopolar type in which a permanent magnet is mounted on the rotor and magnetic flux is passed in the direction of its axis. Therefore, if a general motor is intended to be manufactured using ferrite core, a high flux density at the air gap cannot be obtained, nor a sufficient torque inertia ratio can be attained unless the stacked length of the core is made extraordinarily short. The homopolar type structure has been known as Slosyn, homo-polar type high frequency generator or the like.
A Slosyn type hybrid stepping motor now available in the market uses high flux density material such as Alnico or rare earth as a permanent magnet. Nevertheless, in order to make the stacked length of the core/diameter ratio large, two to three pieces of magnets must be stacked on the core, which requires very difficult manufacturing processes.
FIG. 12 is a cross sectional side view showing the structure of a homopolar type stepping motor, and FIG. 13 is a cross section along the line X-X' of FIG. 12.
Reference number 11 denotes a rotary shaft made of nonmagnetic material, and reference number 12 denotes a cylindrical type permanent magnet of which N and S poles are magnetized in the direction of the rotary shaft. Teeth portions 13 and 14 are provided at opposite sides of the rotary shaft, the permanent magnet and teeth portions being fixed on the rotary shaft 11. The teeth portions 13 and 14 are positioned such that the teeth of one of the teeth portions superpose the grooves of the other of the teeth portions.
Reference number 15 denotes a stator core the outer periphery of which is surrounded with a casing 17, and coils 16 are wound. The stator core 15 is provided with stator salient poles facing the teeth portions 13 and 14 of the rotor, the stator salient pole being provided with a tooth. The rotor teeth portions 13 and 14 and the stator core 15 are made of laminated iron cores. Thus, unless the stacked thickness of the teeth portions 13 and 14 is made thin, a high density of the air gap flux .phi. is not attained.
With the structure of the conventional motor as above, the permanent magnet is mounted remote from the air gap portion between the stator and the rotor. Therefore, the leakage flux is large and the utility of the magnet is poor.
As for the conventional permanent magnet type linear stepping motor, a permanent magnet multi-polarized in the direction of movement has been used as a stator rail. Thus, if a long rail is used, the cost for the rail becomes high. In addition, the need of a protective cover for preventing the attraction of ambient iron particles becomes an issue. Thus, the conventional permanent magnet type liner stepping motor has disadvantages when compared with a hybrid type or variable reactance type linear stepping motor.
The permanent magnet type linear stepping motor as proposed in Japanese Patent Application No. 57-48737 aims to solve the above problems, in which a movable member arrangement is provided sandwiching the rail made of only inductor teeth with an armature electromagnet and a multi-polarized permanent magnet.
FIG. 14 is a cross sectional front view of the device according to the above prior art, and FIG. 15 shows cross sections respectively along the line A-A' and the line B-B' of FIG. 14.
Reference number 101 denotes coils wound about both sides of a yoke 102, reference number 103 denotes a mover with inductor teeth made of magnetic material, reference number 104 denotes a permanent magnet fixedly attached to the yoke 102 facing the movable member 103, and reference number 105 denotes a nonmagnetic material fixed to the movable member 103 for supporting an industrial machine 106.
The repulsion and attraction actions produced between the pole pieces of the inductor teeth on the mover 103 formed by induction of the coil 101 and the pole pieces of the permanent magnet 104, make the mover 103 move in the direction perpendicular to the drawing paper surface in FIG. 14, that is, in the vertical direction in FIG. 15.
As seen from the drawings, two air gaps are formed which result in a complicated structure and a poor quality of the device.
Sawyer hybrid type linear pulse motors are known in the art which are provided with means for commutating currents without brushes by performing a closed loop control of a three phase linear DC motor, that is, a linear pulse motor.
The motor of this kind, however, has a large leakage flux from the cores forming a magnetic path for concentrating magnetic flux of the permanent magnet. Therefore, a large cross section of the magnetic path is required, and the dimension of the whole device is likely to become bulky.